1. Field of the Invention
This invention relates to a caster device, more particularly to an improved caster device which is used for supporting a push cart.
2. Description of the Related Art
Referring to FIG. 1, a conventional caster device 1 is shown to be adapted to support a push cart 10 for carrying books, foods or other heavy things thereon. The conventional caster device includes a mounting member 11 which is fixed to the bottom of the push cart 10. A bolt 12 is welded to the mounting member 11. A rotary member 13 and a retaining member 14 are secured to the mounting member 11 by means of the bolt 12. The bottom face of the mounting member 11 has a first annular ball-receiving groove 111, while a second annular ball-receiving groove 131 is formed correspondingly in the top face of a rotary member 13. The bottom face of the rotary member 13 has a third annular ball-receiving groove 132, while a fourth annular ball-receiving groove 141 is formed correspondingly in the top face of the retaining member 14. A plurality of steel balls 18 are confined rotatably between the first and the second ball-receiving grooves 111, 131, and between the third and the fourth ball-receiving grooves 132, 141. A nut 15 engages the bolt 12, and a pin 16 passes perpendicularly through the nut 15 and the bolt 12 in order to secure firmly the rotary member 13 and the retaining member 12 in position. The rotary member 13 has a pair of support legs 133 depending therefrom. A wheel 19 is disposed pivotally between support legs 133 by means of a rivet 134. As a result, the rotary member 13 can rotate relative to the mounting member 11 due to rotation of the steel balls 18, thereby enabling the user to readily move the push cart 10 in any direction.
It is noted that it is difficult to place heavy things uniformly on the push cart 10. Thus, the push cart 10 will have an unbalanced depression force which is exerted on the rotary member 13. The caster device 1 may have the following problems:
1. Since the diameter of the retaining member 14 is limited by the distance between the support legs 133, the retaining member 14 merely supports a part of the mounting member 11 and the rotary member 13. Thus, the effective supporting area of the retaining member 14 is relatively small. The rotary member 13 will generate a force that bears against the unbalanced depressed movement of the push cart 10. Cooperatively, the design of the first ball-bearing groove 111 and the second ball-bearing groove 131 does not enclose the steel balls 18 and forms a clearance therebetween. Hence, the mounting member 11 will incline to a direction that causes the mounting member 11 to move away from the rotary member 13, thereby forming a larger clearance that easily causes the release of the steel balls 18. Furthermore, sand, mud, and rocks will enter the first and second ball-bearing grooves 111, 131 through the larger clearance, thus resulting in friction between the steel balls 18, the mounting member 11, and the rotary member 13 and in eventual damage to the steel ball 18. Therefore, the user has to change the steel balls 18 very often.
2. Because only the rotary member 13 can bear against the unbalanced force exerted from the caster device 1, the support legs 133 will gradually bend or even break down to reduce the caster device's life time. Besides, when the push cart 10 is in use, damage to the support legs 133 may cause an unstable movement to result in accidents and in things falling from the push cart 10.
3. With reference to FIG. 1, the caster device 1 is not an enclosed design. When the push cart 10 is in use, the wheel 19 may pass through a body of water. Water is easily retained in the annular ball-bearing grooves 131, 141 and prevents the steel balls 18 from being smoothly moved for changing the direction of the push cart 10.
4. The bolt 12 is welded to the mounting member 11 in such a manner that the rotary member 13 and the retaining member 14 are fixed to the mounting member 11 merely by means of the bolt 12. As a result, the unbalanced depression force exerted from the push cart 10 will cause the bolt 12 to split or break.